Burgess Shale

Amiskwia sagittiformis (unknown affinity)

Amiskwia shows us three definite body segments: a head with two prominent tentacles, an unsegmented trunk with stubby side fins, and a flattened tail. The fins and tail suggest this was an active swimmer (also suggested by its rare appearance in the Burgess Shale formation). Walcott first described this fossil in 1911 and assigned it as a chaetognath (arrow worm). However, Amiskwia appears to lack the characteristic grasping spines and teeth of other Burgess Shale fossil arrow worms, so later scientists suggested it was more likely a nemertean (ribbon worm). However, key characteristics of that group are also absent, so Amiskwia remains another of the Burgess Shale weird wonders with no obvious relationship (affinity) to any other living or extinct group. Fossil sizes up to one inch.

Amiskwia

Note that in the fossil preparation the head shows a highly reflective area (cerebral ganglia?). (These are also sketched in above in the artist's rendering.) The broad light area running along the trunk is the gut, while the narrow linear structures along the trunk may be traces of blood vessels and a nerve cord.